Method for forming a metal oxide film

ABSTRACT

A method for forming a capacitor insulation film includes the step of depositing a monoatomic film made of a metal by supplying a metal source including the metal and no oxygen, and depositing a metal oxide film including the metal by using a CVD technique. The method provides the metal oxide film having higher film properties with a higher throughput.

The present invention relates to a method for forming a metal oxide filmand, more particularly, to a method for forming a metal oxide filmhaving excellent step coverage and film qualities with a higherthroughput.

In recent years, as DRAM devices have become more densely integrated,the capacitors used for storing data in the respective memory cells ofthe DRAM have become smaller. Silicon nitride film is generally used asa capacitor insulation film for the structure of the capacitor in theDRAM. The structure of the capacitor has become more complicated and theeffective area of the capacitor insulation film has increased in orderto obtain a sufficient capacitance. However, there is a tradeoff betweensmaller size and greater effective area in the capacitor. Moreover, aslong as silicon nitride film is used as the capacitor insulation film,there cannot be significant increase in the capacitance of thecapacitor.

Therefore, high dielectric materials have been sought for use as thecapacitor insulation film in the DRAMs. In particular, tantalum oxide isexpected to achieve a higher capacitance, and it is researched widely.This is because silicon nitride only has a dielectric constant of about7, whereas tantalum oxide has a dielectric constant of 25 or greater.Thus, tantalum oxide film can be expected to offer an increase ofthreefold or greater in the capacitance of the resultant capacitor.

Until now, a CVD technique has been used to form the capacitorinsulation film. When the CVD technique is used, the substrate on whichthe capacitor insulation film is to be grown is placed inside a reactionchamber, and the substrate temperature is maintained at a specificvalue. Metallic compound gas and O₂ gas are simultaneously supplied intothe chamber, thereby inducing reactions on the substrate to grow thereonthe capacitor insulation film. For example, when forming a capacitorinsulation film made of tantalum oxide film, Ta(OC₂H₅)₅ gas and O₂ gasare simultaneously supplied as the metal sources. Thus, the CVDtechnique enables simple and quick film deposition to form the capacitorinsulation film.

However, when the CVD technique is used, there is a problem in that thefilm thickness becomes less uniform when the surface structure of theunderlying film is complicated. For example, when forming a capacitor,the capacitor insulation film is generally formed onto an underlyingfilm having a complicated step structure. This complicated stepstructure is designed to increase the effective area of the capacitorinsulation film to obtain a larger capacitance in the resultantcapacitor. If a higher reaction rate is used when performing the CVDprocess on this type of the underlying film, the thickness of thecapacitor insulation film becomes less uniform. The less uniformity inthe film thickness is particularly observed near the step of theunderlying film. In other words, step coverage of the capacitorinsulation film will be deteriorated in such a structure. In order tosolve this problem, the CVD process may be performed with a lowerdeposition rate. This approach increases the uniformity of the filmthickness; however, it also becomes difficult to eliminate impurities inthe film. Thus, the concentration of impurities increases in the film todecrease the density of the film, thereby degrading the film qualities.

Furthermore, when the capacitor insulation film is grown using the CVDmethod, a larger incubation time is needed if the underlying film ismade of a material having properties significantly different from thoseof the material of the capacitor insulation film. In the deposition ofthe capacitor insulation film, nuclei are first formed as scatteredacross the underlying film, and then the capacitor insulation film isgrown around the formed nuclei. As such, the thickness of the capacitorinsulation film is different between the areas around the nuclei and theother areas. This makes the thickness of the capacitor insulation filmbecome irregular, and degrades the above-mentioned step coveragequalities. A shorter incubation time, if employed, may allow a moreuniform film thickness to be obtained for the capacitor insulation film;however, it restricts the materials that can be used for the underlyingfilm.

In order to solve the above-mentioned problems, Patent PublicationJP-A-2002-164348 describes a method for forming the capacitor insulationfilm made of tantalum oxide or other dielectric material having a highdielectric constant (high-k material). This method uses an ALD (atomiclayer deposition) technique in which monoatomic layers (or monomolecularlayers) are deposited one at a time to form a film having a desiredthickness. FIG. 7 is a flowchart showing the process of forming acapacitor insulation film made of tantalum oxide in accordance with themethod described in the patent publication.

In the patent publication, in order to form the tantalum oxide film, asilicon substrate is placed inside the reaction chamber, and thesubstrate temperature is set at 300° C., for example. H₂O gas or otheroxidizing gas is supplied into the reaction chamber to oxidize thesurface of the silicon substrate (step A1). This causes an OH group tobind to the surface of the silicon substrate. When this occurs, the OHgroup is chemically bound with the connectors on the silicon substratesurface. Therefore, even when excessive amounts of H₂O gas are supplied,only the monoatomic layer of the OH group can be formed. Thereafter, N₂gas is supplied into the reaction chamber to purge the unreacted H₂O gasfrom the reaction chamber (step A2), and then the reaction chamber isevacuated to vacuum (step A3).

Subsequently, TaCl₅ gas is supplied into the reaction chamber (Step A4).This step replaces the H atoms in the OH group, that is bound to thesurface of the silicon substrate, with the TaCl₄ group in the TaCl₅ gas,thereby forming a single-layer TaCl₄ film bound with the 0 atoms on thesurface of the silicon substrate. N₂ gas is then supplied into thereaction chamber to purge the unreacted TaCl₅ gas from the reactionchamber (step A5), and then the chamber is evacuated to vacuum (stepA6).

Thereafter, H₂O gas is supplied into the reaction chamber (step A7).This replaces the Cl in the TaCl₄ group on the surface of the siliconsubstrate with the OH group in the supplied H₂O gas. N₂ gas is thensupplied into the reaction chamber to purge the unreacted H₂O gas fromthe reaction chamber (step A8), and then the chamber is evacuated tovacuum (step A9).

Step A4 and step A7 each uses a substitution reaction on the surface ofthe silicon substrate to grow the film. This enables a single monoatomiclayer of the tantalum oxide to be grown in a cycle of steps running fromstep A4 to step A9. The capacitor insulation film made of tantalum oxide(Ta₂O₅) can thus be formed by iterating this cycle until the tantalumoxide film has a desired film thickness.

As described above, when the ALD technique is used to form the capacitorinsulation film, the tantalum oxide film can be grown on the siliconsubstrate, one mono-molecule layer at a time. This makes it unnecessaryto form the nuclei for the capacitor insulation film, differently fromusing the CVD technique, and thus enables the capacitor insulation filmto be formed with a uniform film thickness, having excellent stepcoverage and film qualities.

However, when the ALD technique is used, the tantalum oxide film isformed as a single mono-molecule layer at a time, and thus only a lowthroughput is obtained to grow the film. If a tantalum oxide film of 5nm, for example, is to be deposited, a single cycle of procedures fromstep A4 to step A9 takes as long as 1 minute, for example, and thus atotal of 50 minutes is required for the tantalum oxide film as a whole,causing a low throughput.

It may be considered to reduce the time length needed for the one cycle,by reducing the time length for each step. However, if an insufficienttime is allowed to supply the TaCl₄ gas (the metallic compound gas) atstep A4, for example, the mono-atomic TaCl₄ layer cannot be formeduniformly. This causes the resultant tantalum oxide layer to haveirregularities in the film thickness and film qualities. In addition,the film density is reduced to deteriorate the electrical properties ofthe resultant film. Furthermore, if an insufficient time is allowed tosupply the H₂O gas (the oxidizing gas) at step A7, then the impuritiescannot be sufficiently eliminated from the mono-atomic TaCl₄ layer, andthe surface thereof cannot be sufficiently oxidized. Thus, the filmqualities and the electrical properties of the resultant tantalum oxidefilm deteriorate.

Thus, deposition of a capacitor insulation film having excellent filmproperties by using the ALD technique requires a long time compared tothe deposition by the CVD technique which requires about two minutes fordeposition of a capacitor insulation film having the same thickness.Thus, deposition of the capacitor insulation film by using the ALDtechnique is impractical in the mass production of the semiconductordevices.

It is also noted in the ALD technique to form the capacitor insulationfilm that the TaCl₅ gas and the H₂O gas are alternatively supplied fordeposition of each mono-molecule layer, that N₂ gas or other inert gasis used for exchanging the gas in the reaction chamber followed byevacuation of the reaction chamber. This requires complicated changeoveroperation of the valves for the reaction chamber.

SUMMARY OF THE INVENTION

In view of the above, it is an object of the present invention to solvethe above problems and to provide a method for forming a metal oxidefilm having excellent step coverage and film qualities with a higherthroughput in a semiconductor device.

The present invention provides a method for forming a semiconductordevice including the steps of: depositing a monoatomic film including ametal on a base by using a metal source including said metal and nooxygen; depositing a metal oxide film including oxide of said metal onsaid monoatomic film by using a CVD technique.

In accordance with the method of the present invention, the monoatomicfilm deposited on the base allows the metal oxide film depositing stepto obtain a metal oxide film having excellent film properties with ahigher throughput.

The above and other objects, features and advantages of the presentinvention will be more apparent from the following description,referring to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A through 1C are sectional views consecutively illustrating thesteps in the process for manufacturing a capacitor in accordance withthe first embodiment of the present invention.

FIG. 2 is a top plan view showing chambers used to form a capacitorinsulation film in accordance with the first embodiment.

FIG. 3 is a flowchart of the procedures for fabrication of a capacitorinsulation film in accordance with the first embodiment.

FIGS. 4A through 4D are schematic sectional views consecutivelyillustrating chemical reactions during forming the capacitor insulationfilm in accordance with the first embodiment.

FIG. 5 is a graph showing results of TDDB (time dependent dielectricbreakdown) tests performed on capacitor insulation films formed inaccordance with the first embodiment and the conventional technique.

FIG. 6 is a flowchart showing the procedures in a process forfabrication of a capacitor insulation film in accordance with a secondembodiment of the present invention.

FIG. 7 is a flowchart showing the procedures in a process forfabrication of a capacitor insulation film using the ALD technique.

PREFERRED EMBODIMENTS OF THE INVENTION

Hereinafter, the present invention will be described in detail accordingto preferred embodiments thereof with reference to the accompanyingdrawings.

First Embodiment

The present embodiment is an example in which the present invention isapplied to a method for forming a capacitor insulation film made oftantalum oxide film. Referring to FIGS. 1A through 1C, there are shownconsecutive steps of the process for fabricating the capacitorinsulation film according to the present embodiment. Before forming thecapacitor insulation film, an underlying film is formed on which thecapacitor insulation film is to be deposited. As shown in FIG. 1A, afirst interlayer insulating film 12 made of silicon oxide is formed on asilicon substrate 11. Subsequently, a through-hole 13 a is formed in thefirst interlayer insulating film 12 to expose therein a portion of thesilicon substrate 11. Thereafter, the through-hole 13 a is filled withp-doped polysilicon to form a contact plug 13.

Then, as shown in FIG. 1B, a second interlayer insulating film 14 madeof silicon oxide is formed on the first interlayer insulating film 12and the contact plug 13. A cylindrical hole 15 a is then formed in thesecond interlayer insulating film 14 to expose a portion of the firstinterlayer insulating film 12 encircling the contact plug 13.

A HSG (hemi-spherical grain) layer 15 made of p-doped polysilicon isthen formed as a bottom electrode on the second interlayer insulatingfilm 14, where the cylindrical hole 15 a is formed. Using an RTN (rapidthermal nitration) technique, the HSG layer 15 is then nitrided to forma silicon nitride film 16 as the underlying film.

The capacitor insulation film 17 is then formed thereon. FIG. 2 is a topplan view showing a deposition system for depositing the capacitorinsulation film 17 on a wafer. In FIG. 2, the deposition system includesfirst reaction chamber 22 that is used for deposition using the ALDtechnique, a second reaction chamber 23 used for deposition using theCVD technique, and a transfer chamber 24 used for transferring the wafer(substrate) 21 between the first deposition chamber 22 and the seconddeposition chamber 23. The transfer chamber 24 has therein a robot arm25 for carrying the wafer (substrate) 21, and is normally maintained atvacuum. Other devices are not shown in the drawing.

Referring to FIG. 3, there is shown a flowchart illustrating theprocedures in the process for forming the capacitor insulation film inaccordance with the present embodiment. FIGS. 4A to 4D show schematicsectional views of the underlying silicon nitride film 16, on which thecapacitor insulation film 17 is to be formed, during the consecutivesteps shown in FIG. 3. First, the wafer 21 for which the RTN process isfinished is introduced into the first reaction chamber 22. The substratetemperature is maintained at 300° C., and the ambient pressure insidethe first reaction chamber 22 is maintained at 400 Pa, while supplyingH₂O gas at a flow rate of 50 SCCM (standard cubic centimeters perminute) for 10 seconds (step S1). As shown in FIG. 4A, this causes an OHgroup to bind with the surface of the silicon nitride film 16.Thereafter, N₂ gas is supplied at a flow rate of 2 SLM (standard littersper minute) to purge unreacted H₂O gas from the first reaction chamber22, as shown in FIG. 4B (step S2). The first chamber 22 is thenevacuated and maintained at vacuum for 10 seconds (step S3).

Subsequently, TaCl₅ gas is supplied at a flow rate of 50 SCCM into thefirst reaction chamber 22 for 10 seconds (step S4). As shown in FIG. 4C,this replaces the H atoms in the OH group on the surface of the siliconnitride film 16 with the TaCl₄ group in the TaCl₅ gas, thereby forming amonoatomic seed layer of TaCl₄ group with 0 atoms bound to the surfaceof the silicon nitride film 16. The monoatomic seed layer formed in thisprocess exhibits a uniform film thickness and excellent film qualities,similarly to the case where the ALD technique is used to deposit themonoatomic layers. N₂ gas is then supplied at a flow rate of 2 SLM topurge the unreacted TaCl₅ gas from the first reaction chamber 22, asshown in FIG. 4D (step S5). The first chamber 22 is then evacuated andmaintained at vacuum for 10 seconds (step S6).

The wafer 21 is then transferred from the first reaction chamber 22through the transfer chamber 24 to the second reaction chamber 23, wherethe CVD process is conducted. The substrate temperature is maintained at430° C. and the ambient pressure inside the second reaction chamber 23is maintained at 400 Pa while introducing Ta (OC₂H₅)₅ gas at a flow rateof 200 mg/min and O₂ gas at a flow rate of 1.5 SLM into the secondreaction chamber 23 (step S7). This step replaces the Cl atoms of theTaCl₄ group on the substrate surface with O₂ atoms to form a TaO₂ layer.A bulk layer of tantalum oxide is then deposited on top thereof, therebyforming the capacitor insulation film 17 made of tantalum oxide as shownin FIG. 1C.

Since the tantalum oxide film formed using the CVD technique and theseed layer are made of the same substance, a suitable deposition ratecan be achieved in the deposition of the tantalum oxide film evenwithout using a nucleus. For example, only four minutes of gasintroduction achieves deposition of a 10-nm-thick tantalum oxide film.Thereafter, a TiN film 18 or the like is formed on the capacitorinsulation film 17 as a top electrode, thereby achieving the overallstructure of a capacitor 19.

As described above, in the method for forming the capacitor insulationfilm according to the present embodiment, a bulk layer of the tantalumoxide is grown on the seed layer having the same material as the bulklayer. Therefore, it is not necessary to form nuclei scattered around onthe underlying film, differently from the case where the capacitorinsulation film is deposited using the conventional CVD techniquedirectly on the underlying film. In addition, the present embodimentproves a capacitor insulation film is having excellent step coverage andexhibiting excellent film qualities.

The ALD technique is used only at the stage for forming the monoatomicseed layer, followed by the CVD technique to grow the bulk layerthereon. This allows the method of the present embodiment to form thecapacitor insulation film having the higher film properties with ahigher degree of throughput.

In the present embodiment, step S1 through step S6 are performed in thefirst reaction chamber 22, and step S7 is performed in the secondreaction chamber 23, as described above. However, in cases where thefilm deposition temperatures (the substrate temperatures) are onlyslightly different between in step S1 through step S6 and in step S7, itis also possible to perform the operations of step S1 through step S7continuously in one of the reaction chambers 22 and 23. For example, ifthe difference in temperature is 40° C. or less, then it is consideredthat the temperature in the chamber can be changed in a short period oftime. Therefore, a high level of throughput can be maintained even whenthe steps are performed continuously in one of the chambers.

Referring to FIG. 5, there is shown graphs illustrating results of TDDB(time dependent dielectric breakdown) tests performed on the capacitorinsulation film made of tantalum oxide films formed using the CVDtechnique, the ALD technique and the method of the present embodiment,which are used to form respective capacitor insulation films of the samethickness. In FIG. 5, the ordinate represents Weibull distribution, andthe abscissa represents the time (seconds) when the dielectric breakdownoccurs. The dielectric breakdown times of 40 samples (shown at dots) arearranged in sequence of their Weibull distributions for each of thetechniques used. The tests were performed for all of the samples havingcapacitor insulation film of 10-nm thickness, under the conditions withambient temperature of 85° C., and with 4.6 V of stress voltage on thecapacitor insulation film.

In FIG. 5, the capacitor insulation films formed using the method of thepresent embodiment had significantly improved insulation propertiescompared with the capacitor insulation films formed using the CVDtechnique, and had excellent insulation properties substantially similarto those of the capacitor insulation films formed using the ALDtechnique.

In the ALD technique, it is desired to reduce the time length for thecycle of growing a single mono-atomic layer, in order to decrease thetime length for depositing the overall capacitor insulation film.However, in the present embodiment, since the time length required forforming the bulk layer of the capacitor insulation film is not long,there is an advantage that a sufficient time length can be taken for theformation of the seed layer having excellent properties. By forming thebalk layer on top of the excellent seed layer, an excellent capacitorinsulation film can be obtained.

Second Embodiment

The present embodiment is an example in which the present invention isagain applied to the formation of a capacitor insulation film made oftantalum oxide film. The present embodiment is similar to the firstembodiment described above, except that step S1 of the first embodimentis performed in the ambience of active oxygen gas supplied instead ofthe H₂O gas in the reaction chamber.

In the present embodiment, the supply of the active oxygen gas in stepS1 causes oxygen to bind to the surface of the silicon nitride film 16through oxidation. Then, the provision of the TaCl₅ gas in step S4causes the oxygen, that is bound to the surface of the silicon nitridefilm 16, to bind with the TaCl₄ group in the TaCl₅ gas, thereby forminga seed monoatomic layer made of TaCl₄ group bound to the O atoms on thesurface of the silicon nitride film 16. Therefore, in the presentembodiment, as in the first embodiment, the bulk layer made of thetantalum oxide film is suitably grown on top of the seed layer, which ismade of the same material. Therefore, similar effects can be obtained asin the first embodiment without the need of forming nuclei scatteredacross the underlying film.

Third Embodiment

The present embodiment is an example in which the present invention isagain applied to the formation of a capacitor insulation film made oftantalum oxide film. FIG. 6 shows the procedures of the presentembodiment. The present embodiment is similar to the first embodimentexcept that step S1′-step S3′ similar to step S1-step S3 in the firstembodiment are iterated in the present embodiment.

More specifically, in step S1′ of the present embodiment, H₂O gas issupplied after step S6 under the conditions similar to step S1. As aresult, the Cl atoms in the TaCl₄ group are replaced with OH atoms (stepS1′). Then, N₂ gas is supplied under the conditions similar to step S2so as to purge the remaining H₂O gas and the Cl atoms (or HCl gas), thatwere replaced at step S1′, from the first reaction chamber 22 (stepS2′). Then, the chamber is evacuated to vacuum under the conditionssimilar to step S3 (step S3′).

In accordance with the present embodiment, step S1′-step S3′ areperformed after step S6, whereby, the Cl atoms which are bound to the Taatoms are replaced by the OH group in step S1′, the Cl atoms (HCl gas)replaced are removed from the first reaction chamber 22 in step S2′ andstep S3′, and then the process advances to step S7. Therefore,impurities formed by the Cl atoms can be prevented from contaminatingthe capacitor insulation film, and the resultant capacitor insulationfilm has excellent film qualities.

In the examples of the first through third embodiments, TaCl₅ is used asthe metal source therefor. However, It is also possible to use TaF₅,Ta(N(C₂H₅)₂)₃ or the like as the metal source. Furthermore, by using Al,Ti, Hf, or Nb metal alloys as the metal source, it is also possible toform a metal oxide film made of aluminum oxide, titanium oxide, hafniumoxide, or niobium oxide. For example, by using A1(CH₃)₃ as the metalsource, it is possible to form aluminum oxide. By using TiCl₄ orTi(N(CH₃)₂)₄ as the metal source, it is possible to form titanium oxide.By using Hf(N(CH₃)₂)₄, Hf(N(C₂H₅)(CH₃))₄, or Hf(N(C₂H₅)₂)₄ as the metalsource, it is possible to form hafnium oxide. By using NbCl₅, NbF₅, orNb(N(C₂H₅)₂)₃ as the metal source, it is possible to form niobium oxide.

In the first through third embodiments, H₂O gas, or active oxygen gasare used as the oxidizing gas. It is also possible to use O₂, ozone, orN₂O as the oxidizing gas. Alternatively, hydrofluoric acid may also beused to perform hydrofluoric acid processing. Furthermore, in the firstthrough third embodiments, the metal oxide film is formed on the siliconnitride film, which is formed using the RTN technique. However, asimilar method may also be used as in the embodiments to form the metaloxide film on top of a silicon substrate, a polysilicon film, or ametallic film, for example.

Since the above embodiments are described only for examples, the presentinvention is not limited to the above embodiments and variousmodifications or alterations can be easily made therefrom by thoseskilled in the art without departing from the scope of the presentinvention.

1-13. (canceled)
 14. A capacitor comprising: a first electrode; amultilayer insulator film including: a monoatomic insulator filmincluding a metal oxide and overlying said first electrode; and achemical-vapor-deposited (CVD) metal oxide film formed on saidmonoatomic film; and a second electrode formed on said insulator film.15. The capacitor according to claim 14, wherein said multilayerinsulator film further includes an underlying film interposed betweensaid monoatomic insulator film and said first electrode.
 16. Thecapacitor according to claim 14, wherein both said monoatomic insulatorfilm and said CVD metal oxide film include aluminum oxide film.
 17. Thecapacitor according to claim 14, wherein both said monoatomic insulatorfilm and said CVD metal oxide film include tantalum oxide film.
 18. Thecapacitor according to claim 14, wherein both said monoatomic insulatorfilm and said CVD metal oxide film include hafnium oxide film.
 19. Thecapacitor according to claim 14, wherein both said monoatomic insulatorfilm and said CVD metal oxide film include niobium oxide film.
 20. Thecapacitor according to claim 14, wherein said second electrode comprisesa titanium nitride.
 21. A semiconductor device including the capacitoraccording to claim
 14. 22. A method for forming a capacitor insulationfilm in a semiconductor device comprising the steps of: supplyingmaterial gas which provides OH base on an underlying film; depositing amonoatomic film by supplying a metal source including compound gas; andforming a metal oxide film by supplying metal organic compound gas andoxidizing gas using a CVD technique.
 23. The method of claim 22, whereinsaid material gas includes H₂O.
 24. The method of claim 22, wherein saidmaterial gas includes heated H₂O.
 25. The method of claim 22, whereinsaid metal source including compound gas includes at least one compoundselected from the group consisting of TaCl₅, TaF₅, and Ta(N(C₂H₅)₂)₃,and said metal oxide film includes TaO₅.
 26. The method of claim 22,wherein said metal source including compound gas includes at least onecompound selected from the group consisting of Hf(NCH₃)₂)₄,Hf(N(C₂H₅)(CH₃))₄, and Hf(C₂H₅)₂)₄, and said metal oxide film includeshafnium oxide.
 27. The method of claim 22, wherein said metal sourceincluding compound gas includes at least one compound selected from thegroup consisting of NbCl₅, NbF₅, and Nb(N(C₂H₅)₂)₃, and said metal oxidefilm includes niobium oxide.
 28. The method of claim 22, wherein saidmetal source including compound gas includes Al(CH₃)₃, and said metaloxide film includes aluminum oxide.
 29. The method of claim 22, whereinsaid metal source including compound gas includes TiCl₄ or Ti(N(CH₃)₂)₄,and said metal oxide film includes titanium oxide.
 30. The method ofclaim 22, wherein said metal organic compound gas includes Ta(OC₂H₅)₅.31. The method of claim 22, wherein said oxidizing gas includes at leastone gas selected from the group consisting of O₂, active oxygen, ozoneand N₂O.
 32. The method of claim 22, wherein said underlying film iseither silicon substrate, polysilicon film, silicon nitride film ormetallic film.
 33. The method of claim 22, further comprising the stepof supplying oxidizing gas onto a surface of said monoatomic film,between said depositing a monoatomic film step and said forming a metaloxide film step.
 34. The method of claim 34, wherein said oxidizing gasincludes at least one gas selected from the group consisting of O₂,active oxygen, ozone, and N₂O.
 35. The method of claim 22, furthercomprising the step of forming a conductive film on said metal oxidefilm, wherein said steps are used for forming a capacitor including saidunderlying film as a bottom electrode, said metal oxide film as acapacitor insulation film, and said conductive film as a top electrode.